This may sound like a stupid question but I owuld just like to get something straight.

The 86 IROC-Z came out with 190HP is this at the motor or at the rear wheels?

I am 99% sure it is at the motor but just read a post on here and just had to ask as it seemd like he was talking about RWHP stock.

 

That should be a road horsepower rating, not crankshaft or brake horsepower rating. BHP on that engine is probably more like 230, and driveline losses and inefficiencies eat that extra before it gets to the road.

As a side note, it's amazing how much power can be wasted in the tires alone, which is just another reason to maintain tire pressure and alignment. You can switch to fully synthetic engine, transmission, and rear axle oils to gain power (and reliability), then waste it all by having your tires 4 PSI too low. When your tires start getting excessively hot, you know some energy is being used to create that heat. It all adds up.

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Later,
Vader
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Justice and Freedom will Prevail

 

Thanks Vader so 190hp on the rear is not that bad, like you say around 230 at the motor.

 

That is incorrect. Factory HP ratings are made at the crankshaft, with all "accessories" (that means emissions devices, not A/C and power seats and such) installed and operating; and the engine in its "as installed" condition, with full exhaust, the carb and air intake system, water pump, etc. just exactly the same as the ones it would have in a chassis.

So a "190 HP" factory motor should be expected to put somewhere in the neighborhood of 155 HP to the rear wheels, depending on drivetrain losses.

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"So many Mustangs, so little time..."
ICON Motorsports

 

DOH!

Thanks for the correction, RB. I went back and read the post as "1986 IROC" and realized it was a 305 in question.

BTW - When did the ratings go to RWHP? I know the old ratings had been in effect since the '60, installed in the vehicle with all accessories operating. The old Motor manuals used to even have that in the footnotes. I was under the impression the newer models were road horsepowere rated - or is that just in the past couple of years?

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Later,
Vader
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Justice and Freedom will Prevail

 

They're still rated at the crank with all accesories. Take hp rating x 15% for a manual gearbox and take hp rating x 18% for an automatic gearbox. For example, the previous guy with the 86 Iroc rated at 190hp, assuming a 5spd manual would be 190x.85=161.5 rear wheel hp(rwhp).
take care,
Craig
P.S. my 84 with 305HO and 5spd and K&N filter did 185rwhp which means the car should have been rated at 218hp(185/.85)

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84 Z28 305HO, 5spd, 222,000 miles, Edelbrock intake, Hedman headers, low restriction exh(w/cat), K&N air filter, 14.630 at 93.17mph
Del-A-lum front control arm bushings, Moog ball-joints, Energy suspension front sway bar end links, Moog rear sway bar end links, Eibach pro-kit springs, tokico shocks/struts, AU secondary rods
www.indycamaro.com

 

PLEASE tell me that they were giving "road" horsepower in 1991! I would love to think my 240 was at the rear wheels.

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91 TA 5.7 TPI Automatic.
w/WS6 and 3.23 rear.
K&N Air Filter,Hypertech Coil,Moroso Blue Max Wires, Bosch Platinum plugs gapped at .050,
JET fan switch,JET air foil,Dual cats with Flowmaster 3" exhaust (Headers coming soon),GM Performance PROM, Complete PST components on front suspension, Spohn LCAs/Panhard bar.
My car only uses Mobil 1 transmission fluid, oil, and differential fluid.

 

Its never been measured at the rear wheels. The change in the early 70's (73 or 74, cant remember) was due to the accesories and stuff. The earlier engines were tested with basically nothing hooked up to it.

 

Sorry, but I have to disagree. The ratings were changed TO RWHP in the early '70's after insurance companies started penalizing muscle cars. If you examine the HP ratings back then you will find a dramatic decrease in HP ratings for the same engine/vehicle from one year model to the next (I can't remember exactly what year, but '73-'74 sounds real close). The brake HP had not actually decreased, the automakers were just trying to keep sales up so they started using real world figures. I've read this in numerous automotive magazines.

 

That is also incorrect. Factory HP ratings have never been at the drive wheels, before 1971 or after. What happened in 71 was that they changed from rating them with a typical "dyno setup" like 1¾" headers and a Dominator and Victor Jr. and no emissions devices, to rating them as I described above: with the engine "as installed in the chassis". As a result of going from blue-sky to real-world conditions, most V8 engines dropped at least 100 HP. It's not too far different from what would happen if you took your new 383 with AFR heads and a big roller cam, and carried it to the engine dyno and had them run it with their "generic" carb and distributor setup, and they told you it had 450 HP; then you dropped it in your L98 car with the stock TPI and exhaust manifolds, and drove it to the chassis dyno, and discovered you were putting 240 HP to the wheels, which is not much over 300 at the crank.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Since we have a few of the highly knowledgable members in on this thread, I'd like to ask something about drivetraing percentages loss.

When I was growing up and reading HotRod magazine...way, way, way before the internet...heck, even before XT and AT CPU's , I recall HRM doing a dyno with different trannies and rearends, etc. The only thing I could recall was that it took about 25-30 HP to spin a TH350 and about 35-40HP to spin a TH400. There was no percentage loss listed at that time.

What I've always had a hard time understanding is why do is DT loss a percentage and not a constant?

Why does it take 30 hp to turn the drivetrain and accessories on one engine, and 200 hp on another using the same DT and accessories?

I dunno, maybe I've been hanging around farm equipment too much lately

 

Pre-1970 HP was rated, just the engine
with no accessories or dr train. or Gross HP

Post-1970 to present, HP is rated with accessories and dr train. or Net HP

NO factory HORSEPOWER or TORQUE NUMBERS are to the Rear Wheels.

 

i was under the same impression vader was. i thought in 72 or 73, whenever it was, that they started measuring power at the wheels. if you hop over to ls1.com, they all talk about their cars being dyno'd(stock) and getting like 300hp at the wheels. this proves that hp is measured at the flywheel from the factory because those same cars are advertised as 325hp. so yea, power is 'lower' than it used to be in the sixties(as advertised), but its just with all accessories on the motor.

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83 Z28--not a pretty site, sold thank goodness

74 Z28-- 383/400, green on black. pretty clean. FOR SALE!!!

"I wish I was a messenger and all the news was good..I wish I was the full moon shining off a Camaro's hood"

 

Everything else is close, but the year of the change hasn't been correctly identified yet....

Including 1970 and before, it was rated in SAE "Gross" meaning no accessories with a stock engine...no headers, no aftermarket parts, just the stock engine WITHOUT any accessories (meaning A/C, Alternator, water pump, power steering pump)

In 1971 it was a changeover year to SAE "Net" power. Engine statistics were available in both Gross and Net. Net means that all the accessories were bolted on and functioning. This was to simulate real world conditions.

From 1972 to today, the Net ratings have been published.

There has never been any OEM info published on rear wheel horsepower. The reason for publishing the info in Gross numbers was for marketing purposes. They switched for 2 reasons, government regulators were starting to hound the auto manufacturers for "inaccurate" marketing and the government felt that the auto industry was walking the line on false advertising as the real world #'s differed from the advertised #'s. Also, the insurance industry was starting to have high rates on higher horsepower cars.

We will never see a switch to wheel horsepower ratings. Each manufacturer wants the highest amount of HP per car for marketing against other cars in that market segment.

As for the drivetrain loss, must professional shops use 15% with efficient (not slipping) transmissions, either auto or manual...to be on the conservative side, use 20%. Some late model musclecars are producing near their Net rated HP #'s at the rear wheels because the auto industry is down-rating the engines for insurance purposes. If no one can afford the insurance for your car, it won't sell...

-Adam

 

Drivetrain loss isn't a constant amount because it isn't constant. The more power you make, the more power is lost. OEM has never used rear-wheel HP. If it was, a different HP rating would be on manual and auto cars having the same engine.

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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro

 

This is some interesting stuff here!
So from what I understand "NOW" is that the HP raing is at the flywheel so "145 crank hp"-30 for drivetrain bleed=115hp on pavment.
115hp rocket LOL.
Any one know how they measure HP on FWD imports? I would think that there would be less loss of power on a FWD.
SSC

 

OK, with everbody now in agreement about NET
HP being at the flywheel, lets get into Drive Train Loss on a Dyno. I have been told
by three different Dynojet operations that
for Dynojet(ONLY) to figue the following:
This average
15/18 % on Manual Tran
20/25 % on Auto Trans with 22% Being a good number for 700R4 Auto.
And the most common Dyno today is the Dynojet. And Lets not even get into FWD cars.

 

As far as trying to make a correspndence between what an engine does on the engine dyno and what it does in a car on a chassis dyno...

There are certain losses that are totally independent of engine output, constants as it were, and others that are a function of power. In an auto trans, for example, all of the clutch packs that aren't operated at any given moment have all those frictions and steels rubbing against each other; that loss is dependent solely on RPM. On the other hand, if you look at the rear gears, they slide against each other as they move; the harder you push on them, the more resistance they give, so that is an example of a loss that is dependent on engine output. Things like this is what makes it impossible to come up with a universally valid number for how much loss there is on a chassis dyno.

Then there's the problem of differences between the engine's configuration on the engine dyno, and the same thing once it's in the chassis. For those of you who have ever worked around an engine dyno, you are well aware that on the dyno, there's no Y-pipe, catalytic converter, or exhaust system; often there's no air cleaner; the air reaching the intake is at room temperature, not under-hood air temp like you would have with an open element; the cooling system is different (the water pump eats 15 HP or so, so it's not an insignificant matter); and so on. In short, there's no way to completely duplicate chassis conditions on an engine dyno, and all the errors are in favor of making the engine produce more power on the dyno than in the chassis, so engine dyno numbers are meaningless to the extent that the engine will never reach those numbers in its car.

The guy I used last month to chassis dyno my car told me that he has a friend who owns an engine dyno, with whom he works quite often. He says that on a large number of engines that went through the other shop and then came to his chassis dyno after they were installed, the lowest loss (correction - difference between the readings)he has ever seen was 16%; and that was in a circle-track car with an in-out box and a metallic drive. He says he rarely sees less than 25% difference between those 2 numbers and sometimes alot more than that.

In short, there's alot more things that make those 2 numbers different than just drive train losses. IMHO engine dyno numbers are only good for comparing one naked engine to another, not for comparing one engine on the stand to another one in a car; and chassis dyno numbers are the same way, they compare one car/engine combo to another one, not one car to another, or one engine to another. But, since as far as I've noticed most of us don't drive dyno stands — we drive cars — the chassis numbers are the ones that really matter.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Another factor in the dropping of horsepower ratings in the early '70s was the factories started rapidly dropping compression ratios in order to get ready for the "no-lead" gas and other on-coming pollution controls.

An example would be the quadrajet-carbed Impala/big car 454 rated at 390 horsepower in 1970 (there was also a 345 horse version). It had 10.25:1 compression and 500 ft. lbs of torque!

In 1971, it had 8.5:1 compression and was rated at 365 horsepower and 465 torque.

Late in the 1971 model year, and early in 1972 model year, the ratings method changed (as discussed above) and the same 454 was now rated at 270 horsepower with the 8.5:1 compression and 390 torque.

By 1975, that 454 was down to 215 horsepower and 350 torque with 8.15:1 compression. Sad.
jms